The use of high intensity shock waves to comminute renal and urinary calculi has nearly become a Standard procedure in Western Europe and the United States. Extracorporeal shock wave lithotripsy (ESWL) is also being used to destroy gallstones at various hospitals in Europe and at several research centers in the US. Although these systems are in wide spread use, the basic physical mechanisms whereby the stones are comminuted into small pieces are not clearly understood. Recent evidence indicates that acoustic cavitation (a process whereby microscopic voids within the liquid are made to grow and then collapse violently) is probably a necessary condition for stone comminution. An application by the Principal Investigator to NIH to study the role of acoustic cavitation in stone comminution and tissue damage has been funded under a larger Program Project grant, which will deal with the entire lithotripsy issue. The lithotripsy research group in the Acoustics Department at Moscow State (MSU) University has developed a new type of lithotripter that utilizes the principals of optoacoustics and an acoustic lens to generate the focused shock waves used for stone comminution. With this device they have also undertaken a broad study of lithotripsy. We propose a collaboration between the US and Russian groups. This collaboration appears to have significant advantages that would greatly broaden the scope of the parent grant. In particular, the MSU laboratories are greatly limited by lack of modern equipment. This grant would provide them with some much needed instruments that would permit them to undertake a series of experiments that are beyond the scope of the US Parent Grant. A second area of capabilities that is offered by the MSU group is in the area of nonlinear acoustics theory. The Former Soviet Union (FSU) has historically been the international leader of research in this area, and still dominates international conferences on the topic. Moreover, the center of nonlinear acoustics in the FSU has been the Acoustics Institute at MSU, which our proposed collaborator, Prof. Rudenko, now heads. Together with his associates at MSU, his group will be able to perform theoretical studies that would further expand the scope of the Parent Grant to areas that are now inaccessible to the US team. This proposal requests funding for equipment to enable the MSU group to undertake a series of experiments in shock wave propagation and stone comminution, for some accessories to their computers, and for travel support to coordinate our respective efforts. This joint effort promises exciting advances in lithotripsy research for both countries.